The invention relates to a process for the production of morphologically uniform microcapsules that contain peptides, proteins, or other water-soluble biologically active substances as active ingredients, and microcapsules that are produced according to this process.
As is generally known, peptides and proteins represent active ingredients with sizeable pharmacodynamics, which, however, are broken down upon oral administration because of their hydrolysis sensitivity in the acidic environment of the stomach, as well as enzymatic degradation, and thus are partially inactivated in such a way that their action in the gastrointestinal tract is considerably reduced.
Rapid inactivation of proteins and peptides can be observed, however, even after parenteral administration and especially after intravenous administration because of the half-life, which is very often very short. This means that despite sizeable pharmacodynamics and theoretically lower therapeutic dosages, multiple administrations of higher dosages may be necessary, which mean a large burden on the patients.
Suitable formulations that avoid the above-mentioned drawbacks are depot systems in the form of polymer microcapsules or polymer nanocapsules, which are also known extensively for peptides and are described in the literature.
They have the advantages that
Peptides and proteins are protected against rapid inactivation,
lower dosages are pharmacologically effective,
multiple administration can be reduced,
controlled release of peptides and proteins is possible in principle,
the encapsulated active ingredients are transported in a directed manner, and
undesirable side-effects can be reduced.
The known processes for microencapsulation or nanoencapsulation of water-soluble substances can be divided as follows:
Coacervation or emulsion phase separation
encapsulation by spray drying
solvent-evaporation in an organic or aqueous phase.
All processes include the embedding of active ingredients into a biodegradable polymer matrix or copolymer matrix.
Polymers that are known from the literature for this purpose are polyamides, polyanhydrides, polyesters, polyorthoesters, polyacetates, polylactones, polyorthocarbonates, i.a. To date, polylactide-co-glycolide polymers have mainly been used.
Thus, pharmaceutical compositions of water-soluble peptides and proteins in capsule form, which were produced based on coacervation or emulsion phase separation, are known from, e.g., U.S. Pat. No. 4,675,189 (Syntex Inc.), U.S. Pat. No. 4,835,139 (Debiopharm S.A.) and EP 302 582 B1 (Southern Research Inst.).
According to this disclosure, processes are described in which the copolymer that is used, preferably poly-(lactide-co-glycolide)-polymer, is dissolved in a halogenated organic solvent, preferably dichloromethane, and an aqueous peptide solution is dispersed in this solution. Then, a so-called coacervation agent is added. The coacervation agent is soluble in the organic solvent, but the polymer is insoluble in the coacervation agent, causing precipitation of the polymer with the inclusion of the dispersed polypeptides. As a coacervation agent, usually silicone oil is used for phase separation. After the silicone oil is added, a large amount of heptane, which ensures the setting of the microcapsules, must be added as well.
The encapsulation efficiency of this method is approximately 70% (U.S. Pat. No. 4,835,136). The microcapsules that are produced have a diameter of 1 to 500 xcexcm, preferably 10 to 50 xcexcm according to the examples. 
In addition to the use of toxicologically problematic agents such as dichloromethane, heptane, and silicone oil, the drawbacks of this process also include the need to use large amounts of solvent, which results from the encapsulation using coacervation agents, such as silicone oil.
A process that is described in EP-A 315875 (Hoechst AG) for the production of biodegradable microcapsules of water-soluble peptides and proteins is based on the spray-drying process, in which an aqueous peptide or protein solution is emulsified in an organic polymer solution, and this emulsion is spray-dried.
As a biodegradable polymer, a mixture of polyhydroxybutyric acid and poly (lactide-co-glycolide) polymer is used in a mixing ratio of between 99:1 to 20:80.
The peptide or protein is present in micronized form or in an aqueous solution. As a solvent, chloroform, dichloromethane, DMF or a solvent mixture that consists of water/ethanol/chloroform are considered. According to the examples, chloroform is used. The spray drying is carried out at temperatures of between preferably 45 and 95xc2x0 C.
Disadvantageous in this process is the potential risk of explosion when a non-halogenated solvent is used and high temperatures are used simultaneously during the drying process. Moreover, the use of non-flammable solvents such as dichloroethane results in toxicologically harmful residual solvent contamination in the end product. In addition, spray-dried microcapsules basically show a strong tendency to agglomerate; agglomerates of about 100 xcexcm in size are produced.
Microparticles that are produced according to the xe2x80x9csolvent-evaporation-processxe2x80x9d are described in two Canadian Patent Applications CA 2,100,925 (Rhone-Merieux) and CA 2,099,941 (Tanabe Seiyaku Co.).
Usually, with this method, the aqueous peptide or protein solution is dispersed into an organic polymer solution, or active ingredient crystals are suspended in the polymer solution. After a second aqueous phase is added with a surfactant, the polymer solvent is evaporated.
This method is highly variable, and normally W/Oxe2x80x94 or complex W/O/W-emulsions are produced.
According to CA 2,099,941, water-soluble active ingredients and biodegradable polymers are first dissolved in a solvent or a solvent mixture in which they are both soluble. Then, this solvent is removed, and the solid dispersion that is produced is dissolved in an organic solvent that is not water-miscible. The resulting solution (oil phase) is emulsified in an aqueous phase, so that a W/O-emulsion is produced.
Finally, the organic solvent of the oil phase of this emulsion is evaporated.
Concrete examples of the patent relate to poly (lactide-co-glycolide) polymers (PLGA) as a matrix and a hormone (TRH) that releases thyreotropin or its derivatives as an active ingredient, which are first dissolved in a mixture that consists of acetonitrile/ethanol and optionally water, or only acetonitrile, or that consists of acetonitrile and aqueous gelatin, or of dichloromethane and ethanol.
As an organic solvent in the solution of the solid dispersion, dichloromethane or chloroform is used. An aqueous polyvinyl alcohol solution represents the aqueous phase.
The size of the microcapsules is approximately a diameter of 1 to 100 xcexcm, according to the concrete examples about 50 xcexcm to  less than 100 xcexcm.
According to CA 2,100,925, microcapsules of LHRH hormone and analogs are produced by prior dispersion of the LHRH hormone in powder form in two organic solvents, whereby one solvent (above-mentioned dispersion solvent) makes it possible to produce a homogeneous suspension of the pulverized hormone by simple stirring. The second solvent is readily water-miscible and thus makes the microdispersion of the organic phase in aqueous phase possible.
As a second solvent, dichloromethane or, alternatively, chloroform is used. The capsules have a diameter of between 1 and 250 xcexcm. Preferably, the capsules are larger than 50-60 xcexcm.
The morphology of the microcapsules that are thus produced is also very different. As already explained above, the halogenated solvents that are used are toxicologically harmful. In addition, this process also requires sizeable amounts of surfactants.
The object of the invention was to develop a simple and gentle process for the production of morphologically uniform, non-agglomerating microcapsules using toxicologically harmless solvents, which have an encapsulation efficiency of at least 85%, preferably over 90%, and is to yield microcapsules in a size range of 200 nm to 500 xcexcm with a high degree of concentration. In addition, the process is to make xe2x80x9cscaling-upxe2x80x9d possible.